unit: amount used to measure something
meter: basic unit of length or distance
mass: amount of matter in something
gram: basic unit of mass
volume: amount of space an object takes up
liter: basic unit of liquid volume
meniscus: curve at the surface of a liquid in
a thin tube
temperature: measure of the amount of
heat energy something contains
When you measure, you compare an
unknown value with a known value using
standard units. A unit is an amount used to
measure something. The metric system is
an international system of measurement.
Examples of metric units are the gram, the
kilometer, and the liter. In the United States,
the English system and metric system are
both used. Examples of units in the English
system are the pound, the foot, and the
gallon.
Length is the distance from one point to
another. In the metric system, the basic unit
of length or distance is the meter. A meter is
about the length of a doorknob to the floor.
Longer distances, such as the distance
between cities, are measured in kilometers.
A kilometer is 1,000 meters. Centimeters
and millimeters measure shorter distances.
A centimeter is 1/100 of a meter.
A
millimeter is 1/1,000 of a meter. Figure 6
compares common units of length. It also
shows the abbreviation for each unit.
FIGURE 6
Length can be measured with a meter
stick. A meter stick is 1 m long and is
divided into 100 equal lengths by numbered
lines. The distance between each of these
lines is equal to 1 cm. Each centimeter is
divided into ten equal parts. Each one of
these parts is equal to 1 mm.
There is also a more modern form of the
metric system called SI. The letters SI stand
for the French words Systeme International.
Many of the units in SI are the same as those
in the metric system.
The metric and SI systems are both
based on units of 10. This makes them easy
to use. Each unit in this system is ten times
greater than the one before it. To show
change in the size of a unit, you add a prefix
to the unit. The prefix tells you whether the
unit is larger or smaller. For example, a
centimeter is ten times larger than a
millimeter.
FIGURE 5
FIGURE 7 A meter stick is divided into centimeters and
millimeters.
Do you know how people find the area of
the floor of a room? They measure the
length and th width of the rom. Then, they
multiply the two numbers. You can find the
area of any rectangle by multiplying its length
by its width. Area is ex This pressed in
squared units such as square meters(m2) or
square cenitmeters (cm2).
calibrations.
The amount of matter in something is its
mass. The basic metric unit of mass is
called gram (g). A paper clip has about 1 g
of mass.
Mass is measured with an
instrument called a balance. A balance
works like a seesaw.
It compares an
unknown mass with a known mass.
One kind of balance that is commonly
used to measure mass is a triple-beam
balance. A triple-beam balance has a pan.
The balance has three beams. Weights,
called riders, are moved along each beam
until the object on the pan is balanced. Each
rider gives a reading in grams. The mass of
the object is equal to the total reading of all
three riders.
Mass and weight are related; however,
they are not the same. The weight of an
object is a measure of the Earth’s pull of
gravity between Earth and that object.
Gravity is the force that pulls objects toward
the center of Earth. The strength of the pull
of gravity between two objects depends on
the distance between the objects and how
much mass the each contain. So, the weight
changes as its distance from the center of
the Earth changes.
Always read the
measurement at eye level.
If you are using a glass
graduated cylinder, you
will need to read the mark
on the graduated cylinder
closest to the bottom of the
meniscus. A meninscus is
the curve at the surface of a
liquid in a thin tube. A
plastic cylinder does not
show a meniscus.
The volume of solid of
objects is often measured in
cubic centimeters. One
cubic centimeter is the same
as a milliliter (mL)
Look at Figure 11. Each
side of the cube is 1 cm long. The volume of
the cube is 1 cubic centimeter (cm3). Now
look at the drawing of the box in Figure 12.
Its length is 3 cm. Its width is 2 cm. Its
height is 2 cm. The volume of the box can
be found by multiplying length by width by
height. In this case,volume equals 3 X 2 X 2.
Therefore, the volume of the box in Figure 12
is 12 cm3
HANDS-ON ACTIVITY
CALCULATING AREA & VOLUME
You will need 3 boxes of different sizes,
paper, and a metric ruler.
The amount of space an object takes up is its
volume. You can measure the volume of
liquids and solids. Liquid volume is usually
measured in liters. Soft drinks in the United
States often come in 2-liter bottles.
A graduated cylinder is used to measure
liquid volume.
Graduated cylinders are
calibrated, or marked off, at regular intervals.
Look at Figure 10. It shows a graduated
cylinder. On this graduated cylinder, each
small line is equal to 0.05 mL. The longer
lines mark off every 0.25 mL up to 5.00 mL.
However, every graduated cylinder is not
calibrated in this manner. They come in
different sizes up to 2,000 mL, with different
1. Measure the length, width, and height of
each box in centimeters. Record each
measurement in your notes.
2. Calculate the volume of each box.
record each volume on your notes.
3. Find the surface area of each box. Read
each area in your notes.
Practicing Your Skills
4) ALALYZE Which of the three boxes has
the largest volume?
5) CALCULATE How many milliliters of liquid
will fill each box?
6) ALALYZE What is the surface area of the
largest box?
metric unit of temperature. Water freezes at
0 °C. It boils at 100°C.
Scientists working with very low
temperatures use the Kelvin scale. The
Kelvin scale is part of the SI measurement
system. It begins at absolute zero, or 0K.
This number indicates, in theory at least, a
total lack of heat.
If you have a box tht is 10 cm on each
side, its volume would be 1,000 cm3. A liter
is the same as 1,000 cm3. One liter of liquid
will fill the box exactly.
Temperature is a measure of the amount of
heat energy something contains
An
instrument that measures temperature is
called a thermometer.
Most thermometers are glass tubes. At the
bottom of the tube is a wider part, called the
bulb. The bulb is filled with liquid. Liquids
that are often used include mercury, colored
alcohol, or colored water. When heat is
added, the liquid expands, or gets larger. It
rises in the glass tube. When heat is taken
away, the liquid contracts, or gets smaller.
The liquid falls in the tube. On the side of the
tube is a series of marks. You read the
temperature by looking at the marks on the
tube where the liquid stops.
Temperature can be measured on three
different scales.
These scales are the
Fahrenheit (F) scale, the Celscius (C) scale,
and the Kelvin (K) scale. The Fahrenheit
scale is part of the English system of
measurement. The Celsius scale is usually
used in science. Almost all scientists, even
in the United States, use the Celsius scale.
Each unit on the Celsius scale is in degree
Celsius (°C). The degree Celsius is the
FIGURE 14 The Fahrenheit
and Celsius scales.